Metal halides, supported or unsupported, are made by a vapor phase synthesis technique. The resultant halides can be reacted with metal alkyl compounds to make active olefin polymerization catalysts.
Olefin polymerization catalysts usually comprise transition metal halides such as titanium. zirconium or vanadium halides that have been activated by reaction with an alkyl derivative of a metal from Groups I, II or III of the Periodic Table.
Early (coordination) catalyst systems suffered from the serious drawback that catalyst residues often had to be removed from the polymers. The reason for their removal was that the metal halide residues of the system colored the polymers and tended to corrode fabrication machinery during the manufacturing process. In addition, when used with .alpha.-olefins other than ethylene, the early coordination catalysts gave large amounts of stereo-irregular polymer.
One method for overcoming problems with color, corrosion and lack of stereoregularity is to employ more active and stereospecific coordination catalysts that can be left in the polymer at relatively low concentrations. In this regard, it is known that the activity of titanium-containing catalysts can be increased by supporting them on magnesium halides prepared by prolonged grinding of the support or of the catalyst on the support to increase surface area and modify crystal structure before the supported catalysts are reacted with the metal alkyl. Supported catalyst or support particles made by grinding tend to agglomerate and to have broad particle size distributions whereas it is preferred that such catalysts have a narrow particle size distribution to produce low levels of fine polymer particles.
The art has attempted to solve the problems inherent in using catalysts made from mill-ground intermediates in a number of ways. For example, electron-donors, in particular esters of aromatic carboxylic acids or tertiary diamines, are added during grinding of the catalyst component to suppress agglomeration and during polymerization to increase stereospecificity of polymers from .alpha.-olefins other than ethylene.
Another proposed method for increasing catalyst activity with the expectation of lowering the amount of catalyst needed is, for example, by reacting magnesium alkyls such as Grignard reagents or magnesium alkyl-aluminum alkyl systems with transition metal compounds in the absence or presence of other chloride sources and electron donors, or by impregnating magnesium halides or other magnesium salts with transition metal halides.
A variety of metals, in particular Mg, have been used to reduce transition metal compounds according to the stoichiometric equation 2TiCl.sub.4 +Mg.fwdarw.MgCl.sub.2 +2TiCl.sub.3. As disclosed in U.S. Pat. No. 4,194,992. U.K. Pat. Nos. 2,045,779 and 2,046,740, catalysts have been prepared by reducing halides and alkoxides of transition metals in an inert diluent with metal atoms.
Other publications concerned with one or more aspects of high-activity, leave-in, coordination catalyst systems include: U.S. Pat. Nos. 3,891,746; 3,950,269; 4,021,599; 4,121,030; 4,149,990; 4,217,245; 4,262,102; 4,277,589; and 4,331,561; German Pat. No. 2,060,769; and the text by K. J. Klabunde. "Chemistry of Free Atoms and Particles", Academic Press, New York, 1980, chapters 3 and 4.
No publications have been found, however, that disclose vaporization and subsequent condensation of metal halide(s) plus complementary diluent(s). These particles may be used, for example, in the production of high-activity, leave-in coordination catalysts for olefin polymerization. The process of this invention produces particles that have high surface areas, that resist subsequent agglomeration, and that have controllable pore volume distributions. The particles are useful, for example, in polymerizing .alpha.-olefins in high yield, the polyolefins being characterized by high stereospecificities and bulk densities.